USP Firing Problems after upgrades

[sonicninja]

Hi all,
I'm fairly novice in GBB's but just about know my way around one including mag repair etc.

I have a KWA USP .45 which was running perfectly until I installed a shooters design slide. It now seems to fire intermittently, usually firing the first round and then either dribbling out the remaining rounds or not taking any rounds out of the mag at all.

It was initially tested yesterday when it was a little cold but I've run it in colder weathers before the upgrade with no issues.

I'm sure this isn't an uncommon issue so I wonder if you guys could fire some obvious parts/issues to look at and check. One thing I noticed myself was that the plastic nozzle doesn't spring back as well in the new slide, not sure if this might be the issue.

I should also mention the new slide isn't much heavier and I also upgraded the recoil springs.

Cheers all

Keith

[tomson2912882]

Re: USP Firing Problems after upgrades

Have you tried putting the original recoil spring back in and trying again with the new slide?

[sonicninja]

I was considering that but I would be surprised if it worked since the new install springs are SD 150% springs.

[dave38x]

Re: USP Firing Problems after upgrades

The slide may need to wear in - when i fitted a PGC slide to my KSC glock it was stiff as hell to start with, took a 100 rounds or so to loosen up. One area of significant wear was the aluminium above the cylinder/loading nozzle - maybe field strip the gun and see how freely the nozzle moves?

[sonicninja]

The slide barely moved fully to the rear when I first installed it. If the nozzle wasn't moving correctly could this make the slide sluggish and inconsistent when firing on a full mag of gas? This seems to be what's happening.

[sonicninja]

Still looking for help with this guys.

[Chas]

Have you tried checking to see where the nozzle runs against the slide? You can probably smooth that down a bit.
As for the slide being stiff, you could polish own the guide rails a bit.

[sonicninja]

The nozzle didn't (as I originally had the rear sight screw tightened too much) but now it does. It all seems to move freely now but the slide just doesn't seem to be cycling backwards fully so it doesn't have the chance to lock into the slide release groove. No gas vents so I'm presuming that its all going to the right place. Maybe I should shim the mag top rubber nozzle?

[Chas]

Re: USP Firing Problems after upgrades

I don't think that is your problem, I think that the slide is too tight a fit against the rails, you could probably try some wet and dry on the rails (finest grit possible) and see if there is an improvement.
Also does the slide always move fully forwards after a round is fired?

[sonicninja]

I'll try that. Yeah the slide moves fully forward each time (I've had that issue before on a different USP). It is however a little stiff when I remove it for cleaning etc so perhaps you're right. Maybe it just needs to all bed in a little.

[Chas]

any luck?

[sonicninja]

I'm literally playing as I got this message.
I stripped and cleaned it and it has improved. Funnily the slide is not locking back with only one mag out of three. The small section on the mag that pushes up on the slide lock seems undamaged so unsure why this mag is an issue.

[Chas]

Yup, this bit is usually connected to the feeder in the mag and it can get worn down, if you replace the follower it will lock back fine.

[sonicninja]

It looks completely fan as the others, ill replace it anyway.

Cheers!

[Chas]

If the feeder looks the same the spring might have worn down, so can't push the slide stop up.